.TH std::lognormal_distribution 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::lognormal_distribution \- std::lognormal_distribution

.SH Synopsis
   Defined in header <random>
   template< class RealType = double >  \fI(since C++11)\fP
   class lognormal_distribution;

   The lognormal_distribution random number distribution produces random numbers x > 0
   according to a Log-normal distribution:

   \\({\\small f(x;m,s) = \\frac{1}{sx\\sqrt{2\\pi} } \\exp{(-\\frac{ {(\\ln{x} - m)}^{2}
   }{2{s}^{2} })} }\\)f(x; m,s) =

   1
   sx
   √
   2 π

   exp⎛
   ⎜
   ⎝-

   (ln x - m)2
   2s2

   ⎞
   ⎟
   ⎠

   The parameters m and s are, respectively, the mean and standard deviation of the
   natural logarithm of x.

   std::lognormal_distribution satisfies all requirements of RandomNumberDistribution.

.SH Template parameters

   RealType - The result type generated by the generator. The effect is undefined if
              this is not one of float, double, or long double.

.SH Member types

   Member type         Definition
   result_type \fI(C++11)\fP RealType
   param_type \fI(C++11)\fP  the type of the parameter set, see RandomNumberDistribution.

.SH Member functions

   constructor   constructs new distribution
   \fI(C++11)\fP       \fI(public member function)\fP
   reset         resets the internal state of the distribution
   \fI(C++11)\fP       \fI(public member function)\fP
.SH Generation
   operator()    generates the next random number in the distribution
   \fI(C++11)\fP       \fI(public member function)\fP
.SH Characteristics
   m             returns the distribution parameters
   s             \fI(public member function)\fP
   \fI(C++11)\fP
   param         gets or sets the distribution parameter object
   \fI(C++11)\fP       \fI(public member function)\fP
   min           returns the minimum potentially generated value
   \fI(C++11)\fP       \fI(public member function)\fP
   max           returns the maximum potentially generated value
   \fI(C++11)\fP       \fI(public member function)\fP

.SH Non-member functions

   operator==
   operator!=                compares two distribution objects
   \fI(C++11)\fP                   \fI(function)\fP
   \fI(C++11)\fP(removed in C++20)
   operator<<                performs stream input and output on pseudo-random number
   operator>>                distribution
   \fI(C++11)\fP                   \fI(function template)\fP

.SH Example


// Run this code

 #include <cmath>
 #include <iomanip>
 #include <iostream>
 #include <map>
 #include <random>
 #include <string>

 int main()
 {
     std::random_device rd;
     std::mt19937 gen(rd());

     std::lognormal_distribution<> d(1.6, 0.25);

     std::map<int, int> hist;
     for (int n = 0; n < 1e4; ++n)
         ++hist[std::round(d(gen))];

     for (std::cout << std::fixed << std::setprecision(1); auto [x, y] : hist)
         std::cout << std::hex << x << ' ' << std::string(y / 200, '*') << '\\n';
 }

.SH Possible output:

 2
 3 ***
 4 *************
 5 ***************
 6 *********
 7 ****
 8 *
 9
 a
 b
 c

.SH External links

   Weisstein, Eric W. "Log Normal Distribution." From MathWorld — A Wolfram Web
   Resource.
